[Minigame] - Don't be Last

Added: Mercy countdown works, added timer to scoreboard.

Bugfixes for the sidebar and boss bar, clearer admin/player commands

Initial Release LastCall is a Paper minigame: each round, every competing player gets one challenge. If you are the only player who has not completed the task, you get a warning and are eliminated after a few seconds unless you finish in time. Last player standing wins.